Separation of z



Patented Aug. 26, 1947 SEPARATION OF 2,4,6-COLLIDINE FROM NITROGEN BASE MIXTURES Karl Henry Engel, Teaneck, N. J., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application October 26, 1942, Serial No. 463,411

7 Claims. 1

collidine from mixtures thereof with other nitrogen bases.

Pyridine homologs, such as the picolines, lutidines, and collidines, are customarily extracted along with other nitrogen bases from coke oven distillates and other sources of heterocyclic nitrogen bases by means of an aqueous solution of a mineral acid, usually sulfuric acid. After liberation from these acid solutions by means of alkali, the base mixtures thu obtained are customarily fractionally distilled to obtain fractions predominating in a particular base. 2,4,6-collidine fractions may thus be obtained, and fractions are generally taken which boil predominantly within the range of 165-1'73 C. However, these fractions generally contain only about 50% of 2,4,6-collidine, the remainder consisting of other nitrogen bases of boiling range close to 2,4,6-collidine and, not readily separable therefrom by distillation, e. g.,' 3,4-lutidine (boiling point 164-165 0.), 3,5-lutidine (boiling point 169-170 C.), 2,3,6-collidine (boiling point 173- 174 C.). Mixtures of this kind have found limited practical application and areof low economic value. Pure 2,4,6-collidine, however, is a product of considerable commercial interest, being useful, for example, in the preparation of pharmaceutical products and dyes. The purity requirements in these fields are rigid.

As above indicated, the various lutidines, collidines, and other bases present with 2,4,6-collidine in its commercial fractions are not readily separable from the 2,4,6-cllidine by fractional distillation. N0 practical method for separating these closely related compounds has been found in the literature in this field. In the case of other base mixtures, various methods, usually depending upon fractional crystallization of the more common salts of the bases present, e. g., sulfates, chlorates, etc., have been proposed. However, as stated above, for the separation of such closely related nitrogen bases as 2,4,6-collidine, 2,3,6- collidine, and 3,5-lutidine, no known methods have heretofore been practicalf It is an object of this invention to provide a process for separating pure 2,4,6-collidine from mixtures thereof with closely related nitrogen bases not readily separable therefrom bydistillation.

It is a further object of this invention to provide a commercially feasible process for isolating pure 2,4,6-collidine or fractions rich in 2,4,6-collidine from the usual commercial eollidine fractions, particularly from tar base fractions boiling predominantly within the range of about 173 C. and containing 10% or more 2,4,6-co1lidine.

I have discovered that 2,4,6-collidine may be separated in the form of its hydrochloride from other nitrogen bases not readily separable therefrom by distillation, e. g., the isomeric collidines and lutidines of nearly the same boiling points with which the 2,4,6-collidine is generally associated. The expression like-boiling nitrogen bases, with reference to 2,4,6-collidine, is used herein to denote these nitrogen bases not readily separable from 2,4,6-col1idine by distillation, either because of their close boiling points or because of the formation of azeotropic mixtures. I have found that the hydrochloride of 2,4,6-collidine is insoluble in a-mixture of these other bases with which it is associated in close-boiling fractions, and in aromatic, naphthenic or aliphatic hydrocarbon solvents, e. g., toluene or a mixed parafiinic hydrocarbon solvent derived from petroleum.

The process of my invention may advantageously be applied to nitrogen base mixtures Varying from as low as 10% 2,4,6-collidine content up to major proportions of 2,4,6-collidine when such mixtures also contain the like-boiling nitrogen bases referred to above. Upon fractional distillation of the 2,4,6-co1lidine-containing base mixtures recovered from the usual sources of such mixtures, for example coal tar, as above stated, fractions containing about 50% of 2,4,6-

collidine may generally be obtained. Such fractions are preferably employed in the process of my invention. My invention may thus comprise a process in which a tar base mixture'is first fractionated to obtain a fraction containing at least 10%, preferably around 50%, of 2,4,6-001- lidine along with like-boiling bases, and pure 2,4,6-collidine is then separated from this fraction in the form of its hydrochloride.

In a preferred method'of carrying out the process of my invention, a commercial 2,4,6-co1- lidine fraction, suitably a fraction boiling predominantly in the range 1651'73 C. and containing about 50% 2,4,6-collidine, obtained, for example, by fractionally distilling a mixture of crude coal tar bases, is treated either with gaseous hydrogen chloride or with aqueous hydrochloric acid which may advantageously be the inexpensive and readily available technical grade of muriatic acid, This treatment is preferably carried out in the presence of an inexpensive hydrocarbon solvent such as benzene, toluene, a xylene or a petroleum solvent, particularly one boiling in the range of about 70 to 180 C. An amount of hydrogen chloride (which term is used herein to include both gaseous hydrogen chloride and hydrochloric acid) sufficient to react with about 80%-90% of the 2,4,6-collidine present is preferably employed. However, smaller or greater amounts of acid may be employed, if desired. With smaller amounts of acid, a lower yield of 2,4,6-collidine is obtained, while With larger amounts of acid a base mixture enriched in 2,4,6-collidine, rather than the pure base, is the product. The reaction of the base with hydrogen chloride may be carried out at whatever temperature is convenient, e. g., the normally prevailing temperature.

I have found it desirable to crystallize the 2,4,6- collidine hydrochloride in the substantial absence of water, and preferably in the absence of substantial amounts of the lower alcohols, ketones and similar polar compounds. In order to obtain an anhydrous crystallization medium when an aqueous hydrochloric acid is employed, the mixture is heated to refluxing temperature, preferably with a diluent such as toluene present, to remove the water by azeotropic distillation. The distillate is condensed in a side arm trap where it separates into a water layer and an oil layer. The water layer is removed, while the oil layer, containing unreacted base and diluent, where such has been used, is continuously returned to the still. When all, or nearly all, of the water has thus been removed, the still charge is cooled to normally prevailing temperatures to bring about or to complete crystallization of 2,4,6-001- lidine hydrochloride.

The precipitated crystals are then isolated by filtration, e. g., centrifuging, and are freed from adhering unreacted bases by washing with a suitable solvent, e. g., the solvent used as diluent for the precipitation. The crystals are freed from adhering solvent by drying or other means. 2,4,6- collidine is liberated from the crystals thus obtained, for example, by adding an equivalent Weight of alkali to an aqueous solution of the 2,4,6-collidine hydrochloride. The liberated base which separates out from the resulting salt solution is dehydrated (for example, by treating with solid caustic soda) and distilled. I,

The mother and wash liquors may be distilled to recover solvent for reuse in the process and the residual tar bases may then be refractionated to produce various fractions rich in the other bases present in the starting material.

When the process of this invention is applied to a fraction particularly rich in 2,4,6-collidine, it may be advantageous to carry out a step-wise precipitation of the hydrochloride. In that case, a convenient proportion of the 2,4,6-collidine is precipitated as hydrochloride and filtered in one or more preliminary steps. The mother liquor is then subjected to a further treatment with a quantity of hydrogen chloride sulficient to obtain in this step the optimum yieldof pure product.

The following example is illustrative'of the process of 'my invention:

' ous and oily layers.

Distillation Tem perature (Corrected) Volume, m1.

First drop 5 The apparatus used consisted of an acid-resistant reaction vessel, with agitator, a jacket suitable for heating with steam or for cooling with circulating tap water, and a refluxing condenser. Provision Was made for passing distillation condensate through a settling trap which permitted a separation of mixed distillate consistingof aque- Liquids could be withdrawn from the trap or returned to the reaction vessel, as desired.

The reactionvessel was charged with 1000 parts by weight of the crude collidine fraction and gradually mixed with 380 parts by Weight of 35% hydrochloric acid. parts by weight of toluene were added. The completed charge was heated to refluxing temperature. Water which distilled over and condensed with the hydrocarbon vapors was collected in the settling device, whence it was gradually taken 01f until dehydration of the charge was complete, while the remainder of the distillate was returned to the still. Crystallization of the collidine hydrochloride began at an early stage of the dehydration andwas completed by cooling the dehydrated chargeto about 25 C.

The heavy slurry of uniformly small, wellformed crystals was centrifuged. Crystals of 2,4,6-collidine hydrochloride were washed with toluene to free them of adhering uncombined bases. They were dried at about 90 C. to remove toluene, 557 parts by weight of dry material being obtained, equivalent to about 431 parts of 2,4,6- collidine. The crystals sublimed at 240 C.

The crystals were dissolved in about 500 parts by weight of water. 2,4,6-collidine was liberated by adding a solution of parts of sodium hydroxide in 300 parts of water. The liberated base, collected as an upper liquid layer, was separated. A small additional quantity of the base was obtained by distilling from the aqueous sodium chloride solution a relatively small amount of material and saturating the condensate with sodium chloride. The partially dried base was completely dehydrated by addition of dry sodium hydroxide chips. It was then distilled, 415 parts of 2,4,6-collidine being obtained.

Residual free bases, in admixture with toluene, were agitated with 20% aqueous sodium hydroxide solution to neutralize a small quantity of dissolved hydrogen chloride. Toluene was separated by fractional distillation and the free residual bases were distilled.

The 2,4,6-c0llidine obtained by this procedure boiled at 170.4" C., corrected, all of the material boiling within a range of C., and melted at 46 C. Its specific gravity at 25/4' C. was 0.9103, and its refractive index no at 25 C. was 1.4964.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and. not in a limiting sense.

I claim:

1. A process for separating a product enriched in 2,4,6-collidine from a mixture containing this base and other like-boiling nitrogen bases, comprising precipitating 2,4,6-collidine from such mixture in a substantially anhydrous medium in the form of its hydrochloride, separating the precipitated hydrochloride and treating the separated compound to liberate 2,4,6-collidine 2. A process for separating a product enriched in 2,4,6-collidine from a mixture containing this base and other like-boiling nitrogen bases, comprising treating the mixture in a substantially anhydrous medium with an amount of anhydrous hydrogen chloride insufiicient to react with all nitrogen bases present, to precipitate 2,4,6- collidine hydrochloride, and separating the precipitated hydrochloride.

3. A process for separating 2,4,6-collidine from a mixture containing this base and other likeboiling nitrogen bases, comprising treating the mixture in a substantially anhydrous medium with an amount of anhydrous hydrogen chloride suflicient to react with the major part but not all of the 2,4,6-collidine in such mixture, to precipitate 2,4,6-collidine hydrochloride, and separating the precipitated hydrochloride.

4. A process for the production of pure 2,4,6- collidine from a mixture of coal tar bases containing 2,4,6-collidine and other like-boiling bases, which comprises fractionating the base mixture to obtain a cut boiling predominantly within the range of about 165173 C., treating this cut in a substantially anhydrous medium with an amount of anhydrous hydrogen chloride suflicient to react with the major part but not all of the 2,4,6-collidine, in the presence of a hydrocarbon diluent, to precipitate 2,4,6-collidine hydrochloride, separating this precipitate and treating it with alkali to liberate pure 2,4,6- collidine therefrom.

5. In a process for treating a mixture containing 2,4,6-collidine and other like-boiling nitrogen bases to recover 2,4,6-collidine therefrom, the steps which comprise treating said base mixture with an amount of aqueous hydrochloric acid sufficient to react with the major part but not all of the 2,4,6-collidine; refluxing the acid-tar base mixture thus produced, condensing the vapors evolved during refluxing, separating water from the reflux condensate and returning the water insoluble phase to the refluxing mixture until substantially all the water has been thus removed; cooling the thus refluxed mixture from which water has been removed, whereby 2,4,6-co11idine hydrochloride precipitates and separating the precipitate.

6. In a process for treating a mixture containing 2,4,6-collidine and other like-boiling nitrogen bases to recover 2,4,6-collidine therefrom, the steps which comprise treating said base mixture in the presence of a hydrocarbon diluent with an amount of aqueous hydrochloric acid sufficient to react with the major part but not all of the 2,4,6-co1lidine; refluxing the acid-tar base mixture thus produced; condensing the vapors evolved during refluxing, separating water from the reflux condensate and returning the water insoluble phase to the refluxing mixture until substantially all the water has been removed; cooling the thus refluxed mixture from which water has been removed, whereby 2,4,6-coilidine hydrochloride precipitates, separating the precipitate and treating it with alkali to liberate 2,4,6-collidine.

7. In a process for separating 2,4,6-collidine from a mixture containing a predominating amount of 2,4,6-collidine and smaller amounts of other like-boiling nitrogen bases, the steps which comprise treating said base mixture in a plurality of stages and in the presence of a hydrocarbon diluent with aqueous hydrochloric acid; refluxing the acid-tar base mixture in each stage, condensing vapors evolved from the refluxing mixture, separating water from the reflux condensate and returning the water-insoluble phase to the refluxing mixture until substantially all the Water present in the refluxing mixture in that stage has been thus removed; cooling the thus refluxed mixture from which water has been removed after each stage, whereby 2,4,6-collidine hydrochloride precipitates, and separating the precipitate before the next stage of aqueous hydrochloric acid treatment, the total amount of hydrochloric acid used in all stages being suflicient to react with the major portion but not all of the 2,4,6-collidine present.

KARL HENRY ENGEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,965,828 Fox July 10, 1934 2,035,583 Bailey Mar. 31, 1936 2,136,604 Bailey Nov. 15, 1938 2,288,281 Huijser et a1 June 30, 1942 

